feat: read from stdin if argument missing

src/main.rs

@@ -1,7 +1,18 @@
-use std::env;
+use std::{
+    env,
+    io::{self, Read},
+};
 
 mod parse;
 
 fn main() {
-    println!("{:.3}", parse::parse(env::args().nth(1).unwrap().as_ref()));
+    let input = match env::args().nth(1) {
+        Some(s) => s,
+        None => {
+            let mut buf = String::new();
+            io::stdin().read_to_string(&mut buf).unwrap();
+            buf
+        }
+    };
+    println!("{:.3}", parse::parse(&input));
 }

src/parse.rs

@@ -77,7 +77,7 @@ fn nodes_from_str(s: &str) -> Result<Vec<Node>, Error> {
     let mut nodes = Vec::new();
     let mut state = ParsingState::default();
 
-    let is_ignored_char = |c: &char| !matches!(c, ' ' | '&');
+    let is_ignored_char = |c: &char| !matches!(c, ' ' | '&' | '\n');
 
     let filtered_string: String = s.chars().filter(is_ignored_char).collect();